This invention relates to a radio communication apparatus for use in selectively receiving a plurality of call signals indicative of a plurality of call numbers, respectively. The radio communication apparatus may be a radio paging receiver although description will be mainly directed to the radio paging receiver.
The radio paging receiver of the type described includes a receiving circuit for receiving, as a received signal, each of a primary and a secondary call signal, both specific to the receiver. The primary call signal is for use in carrying out a particular call of a possessor of the receiver. The secondary call signal is for use in carrying out a normal call of the possessor. The receiving circuit produces an internal signal whenever the receiving circuit receives each of the primary and the secondary call signals.
The radio paging receiver further comprises a tone generator for generating an audible tone in response to the internal signal with a controllable volume. In order to stop the audible tone, the paging receiver comprises a manually operable switch which is generally called a reset switch. When manually operated by the possessor, the reset switch produces a tone stop instruction signal. Responsive to the tone stop instruction signal, the tone generator stops the audible tone.
For use in making the possessor discriminate between the particular call from the normal call, the audible tone has a particular and a normal volume level which are different from one another. That is, the tone generator is controlled so that the particular volume level is assigned to the particular call and that the normal volume level is assigned to the normal call. Accordingly, it is possible in theory to discriminate the particular call from the normal call by hearing the audible tone.
However, it is actually very difficult for the possessor to discriminate the particular volume level from the normal volume level by the audible tone. Because it is substantially impossible to exactly recognize the particular volume level by hearing only the audible tone without carrying out comparison with the normal volume level.
In addition, the possessor may have a custom of manually operating the reset switch to stop the audible tone as soon as the tone generator generates the audible tone. This makes it impossible for the possessor to judge whether or not the received signal is the primary call signal.